A retro CGA design built around ROM character bitmaps has been repurposed into a far stranger tool: a CGA card that, with a Raspberry Pi Pico 2 feeding it, can generate 60 Hz high‑resolution graphics in text mode—still in one-bit color, but with overlays and e
On older 8-bit computers—and in early PC graphics cards—CGA character drawing was straightforward: the system fetched character bitmaps from ROM. In a clever twist, [GloriousCow] took that built-in habit and turned it into a timing and data pathway the original hardware was never meant to support.
The key move is that the CGA card keeps its character ROM clocking across the whole screen continuously. including areas at the edges where nothing would normally be shown.. Instead of treating that as wasted activity, [GloriousCow] paired the ROM behavior with a Raspberry Pi Pico 2.. The Pico 2 was used to tap the ROM clocking as a synchronization signal. and to inject the pixel data it wanted.
With that setup, the CGA card can display 60 Hz high-res graphics in text mode.. The tradeoff is exactly what you’d expect from leaning on the original character-driven approach: it’s “a very retro one bit color depth.” But the card can also overlay text and graphics at the same time. because the ROM is still present and doing its usual work.
One outcome highlighted from the stunt is a bouncing DVD logo screensaver running on a DOS PC—something that lands as funny and a little surreal because it’s being generated through CGA-era mechanisms, not modern graphics routines. The project comes with a PCB and a promise of more.
The pattern is built into the hardware behavior itself: the CGA keeps clocking the character ROM even where there’s normally nothing to display. and that uninterrupted ROM timing becomes the synchronization signal that makes it possible to inject custom pixel data—leading to 60 Hz high-res graphics in text mode and enabling overlays because the ROM remains in play.
CGA retro computing Raspberry Pi Pico 2 ROM clocking text mode graphics 60 Hz DOS graphics one bit color depth